Automotive vehicle occupant protection system

ABSTRACT

An end of a seat belt is connected to an actuator that can selectively remove a slack from the seat belt. The actuator includes a main actuator unit, a flywheel which provides a maximum inertia effect for a given space, and a cushioning member for decelerating a movement of the moveable end of the seat belt following a certain initial travel of the moveable end. The main actuator unit produces an early rise in the vehicle occupant deceleration, and the cushioning member smoothly connects the time history of the vehicle occupant deceleration to a ride-down condition whereby the deceleration acting on the vehicle occupant is favorably spread over time, and the maximum level of the deceleration can be minimized. The flywheel contributes to a favorable shaping of the time history of the vehicle occupant deceleration.

CROSS REFERENCE TO RELATED PATENTS (PATENT APPLICATIONS)

[0001] Reference should be made to the following commonly assigned priorpatents (copending patent applications), and the contents of thesepatents (patent applications) are hereby incorporated in thisapplication by reference. Our Ref: Patent (Application) Number Issue(Application) Date F650 6,193,296 Feb. 27, 2001 F651 6,1865,74 Feb. 13,2001 F655 6,2030,98 Mar. 20, 2001 F685 6,2541,64 Jul. 3, 2001 F68609/608,669 Jun. 30, 2000 F687 09/648,190 Aug. 23, 2000 F716 09/729,973Dec. 6, 2000 F781 10/005,739 Nov. 6, 2001 F817 unknown F818 unknown F819unknown

TECHNICAL FIELD

[0002] The present invention relates to a vehicle occupant protectionsystem for improving the crash safety of the vehicle.

BACKGROUND OF THE INVENTION

[0003] In recent years, motor vehicles have been often fitted with apretensioner device which positively increases the tension of the seatbelt for restraining the vehicle occupant at the time of a crash andimproves the protection of the vehicle occupant. The deceleration actingon the vehicle occupant who is restrained to the seat by a restraintdevice such as a seat belt starts rising only when the forward inertiaforce acting on the vehicle occupant at the time of the crash hasstarted to be supported by the seat belt. As it is not possible toeliminate a certain amount of resiliency and slack in the seat belt, thedeceleration of the vehicle occupant reaches a peak level only when thevehicle occupant has moved forward a certain distance under the inertiaforce and the elongation of the seat belt has reached its maximumextent. The peak value of the deceleration of the vehicle occupant getsgreater as the forward displacement of the vehicle occupant under theinertia force increases, and is known to be substantially larger thanthe average deceleration of the passenger compartment of the vehiclebody.

[0004] When the relationship between the vehicle body deceleration andthe vehicle occupant deceleration is compared to the relationshipbetween the input and output of a system consisting of a spring (vehicleoccupant restraint device) and a mass (mass of the vehicle occupant), itcan be readily understood that the maximum elongation and time historyof the spring are dictated by the waveform (time history) of the vehiclebody deceleration. Therefore, it can be concluded that the waveform ofthe vehicle body deceleration should be controlled in such a manner thatnot only the average deceleration acting on the vehicle body is reducedbut also the overshoot of the vehicle occupant deceleration due to theelongation of the spring (vehicle occupant restraint device) isminimized.

[0005] In the conventional vehicle body structure, the impact energy isabsorbed by a crushable zone, consisting of an impact reactiongenerating member such as side beams and gaps defined between variouscomponents, provided in a front part of the vehicle body, and thewaveform of the vehicle body deceleration is adjusted by changing theresulting reaction properties by means of the selection of thedimensions and deformation properties of such parts. The deformationmode of the vehicle body other than the passenger compartment at thetime of a crash may also be appropriately selected so that thedeceleration of the passenger compartment of the vehicle body may bereduced, and the deformation may be prevented from reaching thepassenger compartment. Such vehicle body structures are proposed inJapanese patent laid open publication (kokai) No. 07-101354.

[0006] It is important to note that the injury to the vehicle occupantat the time of a vehicle crash can be minimized by reducing the maximumvalue of the acceleration (deceleration) acting on the vehicle occupantwhich is dictated by the waveform (time history) of the vehicle bodydeceleration. It is also important to note that the total amount ofdeceleration (time integration of deceleration) which the vehicleoccupant experiences during a vehicle crash is fixed for the givenintensity of crash (or vehicle speed immediately before the crash).Therefore, as shown in FIG. 6 for instance, the ideal waveform (timehistory) of the vehicle body (seat) deceleration (G2) for theminimization of the vehicle occupant deceleration (G1) should consist ofan initial interval (a) for producing a large deceleration upondetection of a crash, an intermediate interval (b) for producing anopposite deceleration, and a final interval (c) for producing an averagedeceleration.

[0007] The initial interval allows the vehicle occupant to experiencethe deceleration from an early stage so that the deceleration may bespread over an extended period of time, and the peak value of thedeceleration to be reduced. According to a normal vehicle bodystructure, owing to the presence of a crushable zone in a front part ofthe vehicle and a slack and elongation of the restraint system such as aseat belt, it takes a certain amount of time for the impact of a crashto reach the vehicle occupant. The delay in the transmission ofdeceleration to the vehicle occupant must be made up for by a subsequentsharp rise in deceleration according to the conventional arrangement.The final interval corresponds to a state called a ride-down state inwhich the vehicle occupant moves with the vehicle body as a single body.The intermediate interval is a transitional interval for smoothlyconnecting the initial interval and final interval without involving anysubstantial peak or dip in the deceleration. Computer simulations haveverified that such a waveform for the vehicle body deceleration resultsin a smaller vehicle occupant deceleration than the case of a constantdeceleration (rectangular waveform) for a given amount of deformation ofthe vehicle body (dynamic stroke).

[0008] According to the conventional vehicle body structure, the vehiclebody components of the crushable zone start deforming from a part havinga relatively small mechanical strength immediately after the crash, anda part thereof having a relatively high mechanical strength startsdeforming thereafter. As a result, the waveform of the crash reaction orthe vehicle body deceleration is small in an early phase, and then getsgreater in a later phase so that the vehicle occupant decelerationcannot be adequately reduced. To eliminate such a problem, it has beenproposed to obtain a prescribed amount of reaction force by making useof the collapsing of the side beams and to maintain a stable reaction byproviding a plurality of partition walls in the side beams (Japanesepatent laid-open publication (kokai) No. 07-101354). However, suchprevious proposals can only maintain the vehicle body deceleration at anapproximately constant level at most, and are unable to provide a moreeffective deceleration waveform.

[0009] To minimize the adverse effect of the resiliency of the seatbelt, it is known to provide a pretensioner device in association withthe seat belt to positively tension the seat belt at the time of avehicle crash. According to another previously proposed structure, atleast one of the anchor points of the seat belt is attached to a memberwhich undergoes a movement relative to the remaining part of the vehiclewhich tends to increase the tension of the seat belt in an early phaseof a vehicle crash. Such devices are beneficial in reducing the maximumlevel of deceleration acting on the vehicle occupant at the time of avehicle crash, but a device capable of more precise control of thevehicle occupant deceleration is desired.

[0010] Referring to FIG. 7, the vehicle occupant deceleration G1 andvehicle body deceleration G2 correspond to the input and output of atransfer function representing a two-mass spring-mass system consistingof the mass Mm of a vehicle occupant 2, a spring (such as a seat belt),and a vehicle body mass Mv. More specifically, the vehicle bodydeceleration G2 can be given as a second-order differentiation of thecoordinate of the vehicle body mass Mv with respect to time.

[0011] However, in an actual automotive crash, if a three-point seatbelt is used, the shoulder belt portion of the seat belt which can beconsidered as a spring engages the chest of the vehicle occupantcorresponding to the center of the vehicle occupant mass Mm so that theshoulder belt portion can be considered as consisting of two springs,one extending between the chest and shoulder anchor, the other extendingbetween the chest and the buckle anchor.

[0012] If the seat belt is entirely incorporated to the seat, theshoulder anchor and buckle anchor move as a single body, and the twoparts experience an identical deceleration. In such a case, it can beassumed that the seat belt can be given as a composite of two springs,and the deceleration acting on the shoulder anchor and buckle anchor isidentical to the input to the two-mass spring-mass system or the vehiclebody deceleration.

[0013] Now, suppose if the buckle anchor point is fixedly attached tothe vehicle body while the shoulder anchor is capable of movementrelative to the vehicle body as an example in which the two anchorpoints undergo different movements relative to the vehicle body. In sucha case, because the shoulder anchor and buckle anchor experiencedifferent decelerations, the springs cannot be simply combined or thedecelerations acting on the shoulder anchor and buckle anchor cannot besimply equated to the vehicle body deceleration.

[0014] Meanwhile, the external force acting on the chest wholly consistsof the force received from the seat belt. Therefore, if the time historyof the load acting on the seat belt in the direction of decelerationagrees with the time history of the spring load in the two-massspring-mass system, the chest receives the same deceleration waveform asthe response of the vehicle occupant mass of the two-mass spring-masssystem to the optimum waveform of vehicle body deceleration. Thisenables the vehicle occupant to reach the ride-down state in which thevehicle occupant is restrained by the seat belt substantially withoutany delay and the relative speed between the vehicle body and vehicleoccupant is zero (no difference between the vehicle occupantdeceleration G1 and vehicle body deceleration G2).

[0015] To achieve a time history of the seat belt that produces such astate, it suffices if the time history of the average deceleration ofthe shoulder anchor and buckle anchor (or vehicle body) is equal to theoptimum waveform of the vehicle body deceleration. Introducing theconcept of the waveform of average vehicle body deceleration allows anidentical result in reducing the vehicle occupant deceleration ascontrolling the vehicle body deceleration so as to achieve the optimumwaveform to be achieved.

[0016] The early rise in the tension of the seat belt to apply thedeceleration to the vehicle occupant from an early stage can be mostconveniently provided by a pyrotechnical actuator typically using apropellant. Pyrotechnical actuators are widely known in suchapplications as vehicle air bags and pretensioners. However, it wasfound due to the nature of its structure which relies on the generationof high pressure gas that such an actuator alone may not be able toproduce a desired time history of the deceleration of the vehicleoccupant. It was found that the provision of inertia mass prevents anoscillatory movement to the moveable end or vehicle occupant during theactivation of the actuator. The inventors have discovered that such aproblem can be overcome by adding a suitable amount of mass to theactuator end of the seat belt in combination with a cushioning member.

BRIEF SUMMARY OF THE INVENTION

[0017] In view of such problems of the prior art, a primary object ofthe present invention is to provide a vehicle occupant protection systemwhich can improve the protection of the vehicle occupant at the time ofa vehicle crash for a given dynamic stroke or a deformation stroke of afront part of the vehicle body.

[0018] A second object of the present invention is to provide a vehicleoccupant protection system which can maximize the protection of thevehicle occupant with a minimum modification to the existing vehiclebody structure.

[0019] A third object of the present invention is to provide a vehicleoccupant protection system which can maximize the protection of thevehicle occupant without increasing the weight of the vehicle body ortaking up any significant amount of space in the passenger compartment.

[0020] According to the present invention, such objects can beaccomplished by providing an automotive vehicle occupant protectionsystem, comprising: a seat supported on a floor of a vehicle body; aseat belt provided in association with the seat and including a moveableend; an actuator connecting the moveable end of the seat belt to a partof the vehicle body to selectively remove a slack from the seat belt;and a control unit including a deceleration sensor for detecting afrontal vehicle crash meeting a prescribed condition; the actuatorincluding a mass member attached to the moveable end of the seat belt,an arrangement for amplifying an inertia effect of the mass on amovement of the moveable end of the seat belt, and a main actuator unitadapted to move the mass member in a direction to remove a slack fromthe seat belt immediately upon detection of a frontal vehicle crash.

[0021] Thus, upon detection of a crash, the main actuator whichtypically consists of a pyrotechnic actuator increases the restraint ofthe seat belt by moving the moveable end of the seat belt so that adeceleration greater than the average deceleration (vehicledeceleration) is produced in the vehicle occupant. Because the seat beltand vehicle occupant behave as a spring mass system, an oscillatorymotion of the vehicle occupant tends to be induced. Such an oscillatorymotion is obviously undesirable to the end of minimizing the peak valueof the deceleration acting on the vehicle occupant. Therefore, accordingto the present invention, an increased amount of mass is added to thespring mass system to prevent any such undesirable oscillatory motion ofthe moveable end of the seat belt or the vehicle occupant fromoccurring. The provision of the mass member also facilitates the controlof the time history of the output of the actuator to best achieve thedesired acceleration control for the vehicle occupant.

[0022] The system preferably includes a cushioning member fordecelerating a movement of the moveable end following a certain initialtravel of the moveable end. Thus, after the moveable part has moved by aprescribed distance, the movement is prevented by the cushioning memberand an opposite deceleration is produced in the vehicle occupant so thatthe vehicle occupant and vehicle body move as a single body in a finalphase of the crash, and decelerate at the average deceleration. Thisachieves a waveform of vehicle body deceleration suitable for theminimization of the deceleration of the vehicle occupant.

[0023] The anchor points may be provided in appropriate parts of thevehicle body, but all or some of them may be provided on parts of theseat. According to a preferred embodiment of the present invention, toobtain a highly predictable result, the seat belt may comprise threeanchor points including a shoulder anchor, a seat bottom side anchorprovided near a seat bottom on a same side as the shoulder anchor, and abuckle anchor provided near the seat bottom on an opposite side of theshoulder anchor.

[0024] Preferably, the mass member comprises a flywheel which provides alarge amount of inertia without taking up any significant amount ofspace. The actuator may comprise wire including a first end connected toa working end of the main actuator unit, an intermediate part woundaround a rotary shaft having the flywheel integrally or otherwisefunctionally connected thereto, and a second end attached to themoveable end of the seat belt. In particular, by choosing the rotaryshaft to have an appropriate diameter, it is possible to magnify theinertia effect of the flywheel at will. The inertia effect gets greateras the diameter of the rotary shaft is reduced.

[0025] According to a particularly preferred embodiment of the presentinvention, the main actuator unit includes a cylinder integrallyattached to a side of a seat bottom of the seat, a piston slidablyreceived in the cylinder, and a pyrotechnic gas generator provided onone end of the cylinder, the wire being attached to the piston. However,it is also possible to use other sources of energy for the actuatorincluding pre-loaded springs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Now the present invention is described in the following withreference to the appended drawings, in which:

[0027]FIG. 1 is a schematic side view of the outline of the vehicle bodystructure fitted with a vehicle occupant protection system embodying thepresent invention;

[0028]FIG. 2 is an overall perspective view of the seat fitted with thevehicle occupant protection system according to the present invention;

[0029]FIG. 3 is an enlarged sectional view of the vehicle occupantprotection system;

[0030]FIG. 4a is a schematic view of the vehicle body in an initialphase of the crash;

[0031]FIG. 4b is a schematic view showing an intermediate phase of thecrash;

[0032]FIG. 4c is a schematic view showing a final phase of the crash;

[0033]FIG. 5a is a sectional view showing the state of the actuator inan initial phase of the crash;

[0034]FIG. 5b is a sectional view showing the state of the actuator inan intermediate phase of the crash;

[0035]FIG. 5c is a sectional view showing the state of the actuator in afinal phase of the crash;

[0036]FIG. 6 is a diagram showing the waveforms of the vehicle occupantdeceleration and vehicle body deceleration; and

[0037]FIG. 7 is a conceptual diagram showing the relationship betweenthe vehicle occupant, vehicle body and seat belt at the time of avehicle crash.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038]FIG. 1 schematically illustrates the overall structure of avehicle incorporated with a vehicle occupant protection system embodyingthe present invention. The vehicle occupant protection system includes aseat belt 3 for restraining the vehicle occupant 2 to the seat 1. Asshown in FIG. 2 also, the seat belt 3 has three anchor points, and anend of the seat belt is connected to a retractor 4 integrally providedin a shoulder part of the seat 1, another end fixedly attached to a sideof the seat bottom on the same side as the shoulder anchor, and anintermediate part having a tongue plate that is latched to a buckle 6attached to the side of the seat bottom on the other side of theshoulder anchor. Therefore, the vehicle occupant 2 who is seated in theseat 1 is integrally restrained to the seat 1 by the seat belt 3. Theseat 1 is attached to a floor 5 via seat rails la so as to be adjustablein the fore-and-aft direction.

[0039] An actuator 8 is integrally attached to a side of the seat bottomof the seat 1. As also shown in FIG. 3, the actuator 8 comprises acylinder 8 a extending in the fore-and-aft direction, a piston 8 bcoaxially received in the cylinder 8 a, a cylinder cap 8 c integrallyattached to an end (rear end with respect to the vehicle body) of thecylinder 8 a, and a gas generator 8 d connected to the cylinder cap 8 cso as to communicate with the interior of the cylinder cap 8 c. Thefront end of the cylinder 8 b in this case opens out to the atmosphere.The actuator 8 is integrally provided with a bracket 8 j by which theactuator 8 is bolted down to the frame of the seat bottom.

[0040] To the piston 8 b is connected an end of wire 9 which extends outof an opening 8 e provided in the rear end of the cylinder cap 8 c. Theouter end of the wire 9 is wound around a rotary shaft 10 a which isrotatably supported behind the actuator 8 and is integrally andcoaxially provided with a flywheel 10, and then further extends to anextreme end which is connected to a base end of the buckle 6. Therefore,as the piston 8 b is driven forward by the gas generator 8 d and thewire 9 is pulled forward as a result, the wire 9 pulls the buckle 6 inthe direction to increase the tension of the seat belt 3 or therestraint on the vehicle occupant 2 while the intermediate part of thewire 9 wound around the rotary shaft 10 a causes the flywheel 10 torotate. The intermediate part of the wire 9 and rotary shaft 10 a arereceived in a casing 8 f which is attached to the rear end of thecylinder cap 8 c.

[0041] The outer circumferential surface of the piston 8 b is providedwith a reversing preventing ring 8 g which allows the forward movementof the piston 8 b by inclining itself to one side but prevents therearward movement of the piston 8 b by wedging into the innercircumferential surface of the cylinder 8 a.

[0042] A tubular cushioning member 8 i is provided on an outer end of anopening 8 h of the casing 8 f facing the buckle 6 in a coaxialarrangement, and the free end of the tubular cushioning member 8 iopposes the base end of the buckle 6 defining a gap of a prescribeddimension d therebetween. A bellows cover 11 covers the wire 9 connectedto the base end of the buckle 6 and the tubular cushioning member 8 i,and extends between the base end of the buckle 6 and the opposing end ofthe casing 8 f. The bellows cover 11 has an adequate rigidity to supportthe buckle 6 in a substantially fixed manner, but demonstrates aflexible that allows the bellows cover 11 to axially compress so as toaccommodate the movement of the buckle 6 in the direction to increasethe tension of the seat belt 3.

[0043] The actuator 8 described above thus comprises the cylinder 8 a,piston 8 b, cylinder cap 8 c and gas generator 8 d, and is designed toprovide a primary acceleration that increases the restraint on thevehicle occupant 2. The tubular cushioning member 8 i provides asecondary acceleration which controls the acceleration provided by theactuator 8 as will be described hereinafter.

[0044] To the gas generator 8 d is connected a signal line from acontrol unit 12 mounted to an appropriate part (such as the floor 5) ofthe vehicle body and incorporated with a crash sensor which, forinstance, may consist of a G sensor. The crash sensor provides a crashdetecting signal to the gas generator 8 d when a crash meeting aprescribed condition is detected. In response to a crash detectingsignal, the gas generator 8 d instantaneously produces expanding gaswhich is then introduced into the cylinder cap 8 c.

[0045] Referring to FIGS. 4a to 4 c and 5 a to 5 c, the mode ofoperation of the embodiment of the present invention is described in thefollowing by taking an example of a frontal crash onto a fixedstructure.

[0046]FIG. 4a shows a state of an initial phase (interval a of FIG. 6)immediately following the occurrence of a crash. The front end of thevehicle body collapses, and the front ends of side beams 13 integralwith the floor 5 undergo a compressive deformation as shown in thedrawing. The crash sensor incorporated in the control unit 12 detectsthe vehicle body deceleration resulting from the vehicle crash exceedinga prescribed intensity, and the control unit 12 judges the conditionthat is produced. If the control unit 12 judges that the condition meetsthe prescribed criterion, the gas generator 8 d is activated.

[0047] The expanding gas produced from the gas generator 8 d isintroduced into the cylinder cap 8 c as indicated by the arrows in FIG.5a, and the pressure of the expanding gas pushes the piston 8 b in theforward direction with respect to the vehicle body. As a result, thebuckle 6 which is connected to the piston 8 b via the wire 9 startsmoving in the direction to increase the restraint of the seat belt 3 onthe vehicle occupant 2 while the rotary shaft 10 a and flywheel 10 startrotating. The movement of the buckle 6 causes the bellows cover 11 tocollapse, and accelerates as the pressure of the generated gasincreases.

[0048] The early rise in the tension or load acting on the seat belt 3corresponds to an increase in the restraint on the vehicle occupant 2and the deceleration of the vehicle occupant from an early phase of thecrash. The resulting rise in the seat belt load is earlier than thatprovided by a conventional seat belt which is simply secured at threeanchor points in restraining the vehicle occupant from being thrownforward under the inertia force. Therefore, the deceleration of thevehicle occupant is made to rise from a very early part of the crash asindicated by G1 in FIG. 6.

[0049]FIG. 4b shows a state in an intermediate phase of the crash(interval b of FIG. 6). As the collapsing of the front part of thevehicle body progresses, the piston 8 b of the actuator 8 moves furtherforward with respect to the vehicle body as indicated in FIG. 5b. As thepiston 8 b moves further forward, the base end of the buckle 6eventually collides with the cushioning member 8 i, and this deceleratesthe movement of the buckle 6, thereby producing an opposite (forwardwith respect to the vehicle body) acceleration to the vehicle occupant.This produces an effect equivalent to that produced by an accelerationdirected in the opposite direction to the deceleration resultingdirectly from the crash acting on the passenger compartment. To betterachieve such an effect, the effective mass of the flywheel 10 anddiameter of the rotary shaft 10 a as well as the acceleration of theflywheel 10 at the time of colliding with the cushioning member 8 i areappropriately adjusted. It is preferable to design the properties (suchas elongation and spring properties) of the seat belt 3 and theproperties (such as impact absorbing property) of the cushioning member8 i so that the speed and deceleration of the vehicle occupant 2coincide with those of the vehicle body (seat 1) upon completion of theacceleration in the opposite direction acting on the buckle 6 duringthis intermediate phase.

[0050]FIG. 4c shows a state of a final phase (interval c of FIG. 6) ofthe crash. During the final phase, the movement of the buckle 6 isfurther decelerated by the cushioning member 8 i, and the piston 8 beventually comes to a complete stop. As a result, the buckle 6 alsostops moving any further, and is retained at this position until the endof the vehicle crash by virtue of a reversing preventing ring 8 g.

[0051] During this final phase, once the speed and deceleration of thevehicle occupant agree with those of the vehicle body (seat 1), there isno relative movement between the vehicle occupant 2 and vehicle body(seat 1), and the vehicle occupant 2 continues to decelerate as a singlebody with the vehicle body (seat 1). In other words, the maximum valueof the vehicle occupant deceleration G1 can be reduced by achieving aride down state in which the relative speed between the vehicle occupant2 and vehicle body (seat 1) is minimized and the difference between thevehicle occupant deceleration G1 and vehicle body deceleration G2 isminimized.

[0052] Thus, the process described above can substantially reduce thevehicle occupant deceleration by controlling the deceleration producedin the buckle 6 so as to follow the optimum deceleration waveform or bydesigning the actuator 8 so as to produce the optimum decelerationwaveform.

[0053] Thus, according to the foregoing embodiment, upon detection of acrash, the main part of the actuator consisting of a pyrotechnicalactuator increases the restraint of the seat belt by moving the moveablepart provided on the seat serving as a part of the vehicle body so thatthe vehicle occupant is allowed to experience an early rise indeceleration. Then, after the moveable part has moved by a prescribeddistance, the movement is prevented by the cushioning member and anopposite deceleration is produced in the moveable part so that thevehicle occupant and vehicle body move as a single body in a final phaseof the crash, and decelerate at the average deceleration. This achievesa waveform of vehicle body deceleration suitable for the minimization ofthe deceleration of the vehicle occupant. As a result, not only asubstantial reduction in the vehicle occupant deceleration can beachieved with a smaller vehicle body deformation (dynamic stroke) butalso the displacement of the vehicle occupant in the passengercompartment relative to the vehicle body can be reduced even more thanpossible by providing a load limiter in the restraining device to reducethe vehicle body deceleration. The smaller displacement of the vehicleoccupant reduces the possibility of a secondary collision.

[0054] When an end of the seat belt is attached to the seat, and anintermediate part of the seat belt is attached to the moveable part viaa buckle, the vehicle occupant and seat can be joined integrally to eachother by using a conventional three-point seat belt incorporated to aseat so that the cost of the system can be minimized without requiringany substantial change to the existing system.

[0055] Although the present invention has been described in terms of apreferred embodiment thereof, it is obvious to a person skilled in theart that various alterations and modifications are possible withoutdeparting from the scope of the present invention which is set forth inthe appended claims. For instance, all or some of the anchor points maybe provided on parts of the vehicle body other than those on the seat.The actuator also may consist of actuators other than pyrotechnicactuators such as spring loaded actuators without departing from thespirit of the present invention.

1. An automotive vehicle occupant protection system, comprising: a seatsupported on a floor of a vehicle body; a seat belt provided inassociation with said seat and including a moveable end; an actuatorconnecting said moveable end of said seat belt to a part of said vehiclebody to selectively remove a slack from said seat belt; and a controlunit including a deceleration sensor for detecting a frontal vehiclecrash meeting a prescribed condition; said actuator including a massmember attached to said moveable end of said seat belt, an arrangementfor amplifying an inertia effect of said mass on a movement of saidmoveable end of said seat belt, and a main actuator unit adapted to movesaid mass member in a direction to remove a slack from said seat beltimmediately upon detection of a frontal vehicle crash.
 2. An automotivevehicle occupant protection system according to claim 1, wherein saidactuator further comprises a cushioning member for decelerating amovement of said moveable end following a certain initial travel of saidmoveable end.
 3. An automotive vehicle occupant protection systemaccording to claim 1, wherein said seat belt comprises three anchorpoints including a shoulder anchor, a seat bottom side anchor providednear a seat bottom on a same side as said shoulder anchor, and a buckleanchor provided near said seat bottom on an opposite side of saidshoulder anchor.
 4. An automotive vehicle occupant protection systemaccording to claim 3, wherein all or part of said anchors are attachedto corresponding parts of said seat.
 5. An automotive vehicle occupantprotection system according to claim 1, wherein said mass membercomprises a flywheel.
 6. An automotive vehicle occupant protectionsystem according to claim 5, wherein said actuator comprises wireincluding a first end connected to a working end of said main actuatorunit, an intermediate part wound around a rotary shaft having saidflywheel functionally attached thereto, and a second end attached tosaid moveable end of said seat belt.
 7. An automotive vehicle occupantprotection system according to claim 6, wherein said main actuator unitincludes a cylinder integrally attached to a side of a seat bottom ofsaid seat, a piston slidably received in said cylinder, and apyrotechnic gas generator provided on one end of said cylinder, saidwire being attached to said piston.
 8. An automotive vehicle occupantprotection system according to claim 1, wherein said actuator isprovided with a member for preventing a reversing movement of saidactuator.